As optical recording media, there have been known, among others, compact discs (CDs), recordable compact discs (CD-Rs), rewritable compact discs (CD-RWs), and as those offering higher recording densities, digital versatile discs (DVDs) and recordable DVDs. To record and play back, among these recording media, at least DVDs, CDs, CD-Rs, and CD-RWs, it is necessary to use, as the light source for optical pickups, one capable of emitting laser light of wavelengths 650 nm and 780 nm.
The laser light of a wavelength of 650 nm is for playback of DVDs, and the laser light of a wavelength of 780 nm is for playback of CDs and for recording and playback of CD-Rs and CD-RWs. The laser light of a wavelength of 650 nm may be used for recording of recordable DVDs. On the other hand, the recent demands for faster recording have been requiring higher-output light sources.
As a light source for incorporation in an optical pickup, there has been known a two-beam semiconductor laser device that can emit a laser light of wavelengths 650 nm and 780 nm from a single package. By incorporating a two-beam semiconductor laser device into an optical pickup, it is possible to make the optical pickup compact and to simplify the assembly thereof.
FIG. 6 and FIG. 7 are a front view and a perspective view respectively, showing a substantial part of a conventional two-beam semiconductor laser device. The two-beam semiconductor laser device 50 has a two-beam semiconductor laser element LDC mounted on a submount 63. The two-beam laser element LDC is integrated on a single substrate 51, with a first semiconductor laser element LD1 and a second semiconductor laser element LD2 formed separately from each other.
The substrate 51 is formed of, for example, n-type GaAs. The first semiconductor laser element LD1 is formed of, for example, an AlGaInP semiconductor, and outputs laser light of a wavelength of 650 nm. The second semiconductor laser element LD2 is formed of, for example, an AlGaAs semiconductor and outputs a laser light of a wavelength of 780 nm. The specific details of the structures of the first, AlGaInP, semiconductor laser element LD1 and the second, AlGaAs, semiconductor laser element LD2 are disclosed in Patent Publications 1 and 2, and therefore, in this respect, only a brief description thereof will be given below.
The first, AlGaInP, semiconductor laser element LD1 has an n-type AlGaInP semiconductor layer 52 formed on the n-type GaAs substrate 51. On the n-type AlGaInP semiconductor layer 52, a p-type AlGaInP semiconductor layer 53 is formed with a first junction layer 54 laid in between. The first junction layer 54 contains a single-quantum-well (SQW) or multiple-quantum-well (MQW) structure, and has part thereof formed into a first light-emitting portion 55.
Likewise, the second, AlGaAs, semiconductor laser element LD2 has an n-type AlGaAs semiconductor layer 56 formed on the n-type GaAs substrate 51. On the n-type AlGaAs semiconductor layer 56, a p-type AlGaAs semiconductor layer 57 is formed with a second junction layer 58 laid in between. The second junction layer 58 contains the same structure as the first junction layer 54, and has part thereof formed into a second light-emitting portion 59.
On the back face of the substrate 51, an n-side common electrode 60 is formed. On the top face of the first semiconductor laser element LD1, a first p-side electrode 61 is formed. On the top face of the second semiconductor laser element LD2, a second p-side electrode 62 is formed.
On the face of the submount 63 to which the two-beam semiconductor laser element LDC is fixed, a first electrode pad 64 and a second electrode pad 65 are formed separate from each other by patterning. The first and second p-side electrodes 61 and 62 of the two-beam semiconductor laser element LDC are fixed to the first and second electrode pads 64 and 65, respectively. This configuration enables the first and second semiconductor laser elements LD1 and LD2 to be driven individually.
The two-beam semiconductor laser element LDC has a so-called junction-down structure; that is, it has the first and second junction layers 54 and 58 located close to the submount 63. This enables the first semiconductor laser element LD1 and the second semiconductor laser element LD2 to dissipate heat efficiently. Thus, the submount 63 serves as a heatsink, and thereby helps stabilize the operation of and increase the output of the two-beam semiconductor laser element LDC.
Behind the two-beam semiconductor laser element LDC on the submount 63, a photodetector 66 such as a photodiode is fitted. According to what is detected by the photodetector 66, the light emission output of the two-beam semiconductor laser element LDC is controlled.
The submount 63, on which the two-beam semiconductor laser element LDC is fixed, is fixed to a heatsink plate or a leadframe (not shown), and to the n-side common electrode 60 of the two-beam semiconductor laser element LDC, a wire 67 is connected at one end thereof. One end of a wire 68 and one end of a wire 69 are connected to the first electrode pad 64 and the second electrode pad 65, respectively. One end of a wire 70 is connected to the photodetector 66. The other ends of the wires 67 to 70 are connected to lead terminals (not shown). In this way, the two-beam semiconductor laser device 50 is fabricated.
In the two-beam semiconductor laser device 50 structured as described above, the first semiconductor laser element LD1 can be driven independently by passing a current between the first p-side electrode 61 and the n-side common electrode 60; the second semiconductor laser element LD2 can be driven independently by passing a current between the second p-side electrode 62 and the n-side common electrode 60. Thus by driving the first semiconductor laser element LD1, laser light of wavelength of 650 nm can be produced, and by driving the second semiconductor laser element LD2, laser light of wavelength of 780 nm can be produced.
Known semiconductor laser devices typically use can packages or frame packages. In a semiconductor laser device using a can package, leads are fitted one-by-one to a metal stem, and a laser element is mounted on the metal stem and is sealed with a cap. In a semiconductor laser device using a frame package, a semiconductor laser element is mounted on a metal frame, and these are then insert-molded. Semiconductor laser devices using frame packages have been attracting attention for their low cost and good mass productivity.
Compared with conventionally widely used semiconductor laser devices using can packages, however, semiconductor laser devices using frame packages offer poorer heat dissipation. For this reason, semiconductor laser devices using frame packages are now mostly used for infrared laser devices. Further improvements are required so as to make semiconductor laser devices using frame packages usable as high-output laser devices for use with CD-Rs and CD-RWs, red laser devices for use with DVDs, two-wavelength laser devices, or blue laser devices operating at high operating voltages.
Patent Publication 3 discloses a semiconductor laser device using a frame package in which such an improvement has been made. FIG. 8 and FIG. 9 are a perspective view and a front view, respectively, of this type of semiconductor laser device using a frame package. FIG. 10 is a sectional view taken along line X-X′ shown in FIG. 9.
In the semiconductor laser device 80, a submount 83 is arranged in a fixed position on the top face of a frame 82. A semiconductor laser element 84 is arranged in a fixed position on the top face of the submount 83. The frame 82 is formed of a metal having good thermal and electrical conductivity, such as copper, iron, or an alloy of either, and is formed into a plate. The frame 82 includes a main frame 86 on which the semiconductor laser element 84 is mounted and sub frames 87 and 88 for wiring that are independent of the main frame 86. The main frame 86 and the sub frames 87 and 88 are integrated into a frame package by being molded in a resin-molded member 85 that is electrically insulative.
The main frame 86 includes an element mount portion 86a, a lead portion 86b and wing portions 86c and 86d. On the element mount portion 86a, the submount 83 is mounted. The lead portion 86b serves as a current path. The wings 86c and 86d are formed to project to the left and right, respectively, for the purpose of heat dissipation and positioning. In the main frame 86, a thick-walled section 86e and a thin-walled section 86f are formed. The thick-walled section 86e is formed by thickening a front part of the element mount portion 86a and front parts of the wing portions 86c and 86d. The thin-walled section 86f is formed by thinning the lead portion 86b and rear parts of the wing portions 86c and 86d. 
The sub frames 87 and 88 are formed to be thin-walled like the lead portion 86b. This enables the lead portion 86b and the sub frames 87 and 88 to be finely processed with ease when the frame 82 is punched out by pressing. Therefore, it is possible to make the semiconductor laser device 80 compact by keeping the intervals between the lead portion 86b and the sub frames 87 and 88 short.
The resin-molded member 85 is formed by insert molding in such a manner that it sandwiches the frame 82, from above the front face and below the back face of the frame 82. On the front face of the resin-molded member 85 is formed a laser output window 85a through which laser light is emitted, as well as an enclosure 85b that is U-shaped so as to be open frontward. Taper faces 85c are formed in front-end parts of left and right side portions of the enclosure 85b. The taper faces 85c permit the semiconductor laser device 80 to be inserted smoothly to be arranged in a predetermined position. The back face of the resin-molded member 85 is formed to be a flat surface 85d that covers the element mount portion 86a, and has substantially the same outer shape (hexagonal shape) as the enclosure 85b located on the front face of the resin-molded member 85.
The resin-molded member 85 does not cover the part of the element mount portion 86a of the main frame 86 in the enclosure 85b, nor does it cover the sub frames 87 and 88. Thus, in these locations, the surfaces of the main frame 86 and the sub frames 87 and 88 are exposed. On the exposed part of the element mount portion 86a, the semiconductor laser element 84 is arranged and fixed, with the submount 83 placed in between. Subsequently, the semiconductor laser element 84 is connected to the main frame 86 with a wire (not shown), and the submount 83 is connected to the sub frames 87 and 88 with wires (not shown).
The submount 83 is built as a light receiving element whose base material is Si. This makes it possible to monitor the light emitted from the rear face of the semiconductor laser element 84. Instead of Si, a ceramic or metal material that has high thermal conductivity may be used, such as AlN, SiC, or Cu. The submount 83 is fixed to the element mount portion 86a, for example, with a solder material such as Pb—Sn, Au—Sn, or Sn—Bi, or with Ag paste. The semiconductor laser element 84 is fixed to the submount 83, in a predetermined position thereon, for example, with a solder material such as Au—Sn or Pb—Sn, or with Ag paste.
Structured as described above, the semiconductor laser device 80 using a frame package offers the following advantages: since the surface of the semiconductor laser element 84 is exposed, it offers good heat dissipation; it has a simple structure, and is therefore suitable for mass production.    Patent Publication 1: JP-A-H11-186651 (Claims, paragraphs [0017] to [0023], FIG. 1)    Patent Publication 2: JP-A-2002-329934 (Claims, FIG. 1, FIG. 4)    Patent Publication 3: JP-A-2002-43679 (paragraphs [0010] to [0022], FIG. 1, FIG. 2, FIG. 4)